Our previous studies in this project demonstrated that all aspects of LH secretion are dependent on the brain peptide, LHRH (GnRH), but that FSH secretion has two components: basal FSH secretion which is dependent on a LHRH sensitive component and pulsatile FSH secretion which is independent of LHRH and is probably regulated by a putative FSH-releasing hormone. Two candidates for these FSH- affecting components, recently discovered by recombinant DNA methodology, are a peptide that we have demonstrated previously to be a portion of the LHRH prohormone and a gonadal factor termed inhibit. We have produced antiserum against both of these new factors. In studies of the LHRH prohormone, we have demonstrated that the synthesis and processing of the LHRH prohormone is dependent on gonadal steroids. Studies to determine the significance of bioactivity associated with processed fragments of the prohormone are ongoing. Using the inhibit antiserum, we have localized inhibit in testicular Sertoli cells and ovarian granulosa cells. Ongoing studies with cultured rat Sertoli cells are revealing the mechanisms that regulate inhibit secretion. Using the antiserum to neutralize endogenous inhibit in vivo we demonstrated that inhibit affects only the basal aspects of FSH secretion. Neutralizing inhibit at different ages, we have demonstrated that endogenous inhibit actively suppresses FSH secretion prior to, but not after, puberty in the male and only after the initiation of puberty in the female. Restructuring of the inhibit subunits produces an FSH-releasing factor termed activin. We have very recently produced antiserum against activin and have begun studies to determine the physiology of this factor. The results from these studies have already redefined long standing concepts of the mechanisms regulating gonadotropin secretion and will continue to advance our understanding of these mechanisms in the future.